Because of the increasing operational speeds of semiconductor integrated circuits, conventional electrical interconnect systems for transmitting data between such higher speed integrated circuits has become inadequate. The maximum speed of electric signals along conductors is achieved by using air as the dielectric medium which has a dielectric constant of one. In addition, interconnect distance should be as short as possible which requires a high density of conductor lines per unit area. Another factor affecting the speed of signals along interconnect lines is the resistive losses in small cross-sectional area lines. Also, in order to preserve pulse shape and minimize signal distortion, it is desirable to use controlled impedance transmission lines as interconnects.
Therefore, it is important to provide an interconnect fabrication sequence to produce an interconnect system having the following features: (1) high density providing short interconnect paths, (2) lowest dielectric constant possible, (3) low resistance conductors, (4) controlled, matched impedance interconnects, (5) minimum impedance discontinuities, and (6) highest possible fabrication yield process.
The present invention discloses a method of fabricating a very high density electrical interconnect system which provides simplicity of fabrication for high yield along with flexibility of material selection to facilitate integration of the substrate into a variety of complete systems with varying performance criteria to maximize the above-described features.